Managing arrhythmias is challenging in patients who have undergone heterotopic heart transplantation because of the superimposed rhythms of the native and donor hearts. We present the case of a 43-year-old man with a previously placed biventricular pacemaker who underwent heterotopic heart transplantation and later developed acute rejection of the donor heart, which led to bradycardia and pause-dependent ventricular fibrillation. The patient remained clinically stable in the short term, likely because of partial recovery of myocardial function in the native heart. He later underwent placement of a pacing lead in the donor heart, allowing linking of the two hearts via a biventricular pacemaker.